1. Field of the Invention
The invention is related to an apparatus and methods for determining how long a patient has been experiencing a medical condition. Specific embodiments of the invention can be used to determine the approximate length of time that a patient has been experiencing abnormal blood sugar level fluctuations and thus how closely or often that patient should be tested for diabetes.
2. Background of the Related Art
There are many devices and methods for determining whether a patient has a particular medical condition. However, there are few devices or methods for determining how long the patient has been experiencing the particular medical condition. As a specific example, there are several tests for determining whether a patient has diabetes, but there no devices or methods that are configured to determine how long the patient has been experiencing the diabetic condition.
A diabetic person's body has difficulty regulating blood sugar levels. As a result, a diabetic's blood sugar level fluctuates greatly during each day depending on diet and level of exercise. The effects of these blood sugar level variations are not immediately apparent and tend to build up over time. Early stage complications of diabetes can include vision and circulatory problems. Typically, these early stage complications do not become apparent until a patient's blood sugar level has been out of control for seven to ten years. Thus, it is common for a patient to be approaching the onset of diabetes for many years before diabetes is actually diagnosed.
There are few tests for predicting or determining whether a patient has diabetes (diagnosing diabetes) before actual symptoms begin to appear. One such test is a glucose tolerance test. In this test, a patient ingests a prescribed amount of glucose, and the patient's blood is then periodically sampled and tested to determine the patient's blood sugar level as the patient metabolizes the glucose. However, some patients that show abnormally elevated blood sugar levels during such a test fail to subsequently develop diabetes, thus calling into question the reliability of the test.
A second diagnostic test, called the Islet Cell Antibody (ICA) test, can be used to predict whether a patient will develop Type I diabetes. This test can predict the onset of diabetes by as much as five years before actual symptoms appear. The ICA test, however, is rarely performed because of its complexity, expense and lack of specificity. Furthermore, this test is only useful for predicting Type I diabetes, which only occurs in approximately ten percent of the diabetic patient population.
U.S. Pat. No. 5,203,328 discloses another apparatus and method for determining whether a patient has diabetes. The system and method measure characteristics of the patient's eye that are indicative of diabetes. Specifically, the system and methods illuminate ocular tissue in a patient's eye, and measure backscattered light and fluorescent radiation generated by the ocular tissue in response to the excitation light. The intensity of the backscattered light and fluorescent light at particular wavelengths are then used to determine whether the patient has diabetes. The contents of U.S. Pat. No. 5,203,328 is hereby incorporated by reference.
Similarly, U.S. Pat. Nos. 4,895,159 and 4,883,351 disclose systems and methods for detecting the existence of diabetes using only backscattered light. The contents of these patents are also hereby incorporated by reference.
Although the systems and methods described above can determine whether a patient has been experiencing the symptoms of diabetes, none of the systems or methods are capable of determining how long the patient has been experiencing the diabetic symptoms.
Once it becomes apparent that a patient may possibly develop diabetes, doctors will ask the patient to return for more tests on a periodic basis to determine whether the patient's condition actually develops into the disease. Doctors have certain protocols about how long a patient should wait before being recalled for more testing. If a patient has few symptoms suggestive of diabetes, the patient may not be recalled from more than a year. If several suggestive symptoms are present, the doctor may wish to recall the patient after only a few months. Unfortunately, there is no diagnostic tool for accurately predicting how long a patient may have been experiencing diabetic symptoms, or for determining how great the patient's risk of actually developing the disease. If such a tool were available, it would enable a doctor to tailor his recall and therapy pattern to a patient's needs.